In general, photolithography is a process of irradiating light onto a semiconductor wafer through a mask having a circuit pattern to be formed so as to transfer the circuit pattern from the mask to a photoresist, i.e., a technique for forming a fine pattern at a desired portion using a light source, and an exposure apparatus is an apparatus for performing the process. The exposure apparatus is frequently used not only in semiconductor industries but also in various display industries.
The exposure apparatus can be divided into proximity exposure, projection exposure, maskless exposure, etc. according to exposure methods. The maskless exposure is a method performed by removing a photomask commonly employed in the exposure methods.
Under the recent market situation of flat panel displays (FPDs), printed circuit boards (PCBs), etc., studies have been conducted to develop large-sized and high-definition FPDs, PCBs, etc. However, improvements are required in many fields so that the maskless exposure apparatus comes into the spotlight under the market situation.
The most difficult problem to be solved is a problem of an optical system included in the maskless exposure apparatus. The optical system is configured to include a light source unit for irradiating light, a unit for adjusting the angle of light, a light condensing unit, a unit for increasing the resolution of light, etc.
In an optical system of a related art maskless exposure apparatus, a large-sized substrate should be carried at a high speed in order to perform exposure while scanning the substrate without any mask, and the exposure should be performed while scanning more pixel data several times in order to implement a higher-definition pattern. However, existing digital exposure apparatuses convert a predetermined light source into spots and irradiate the spots in an array form. Therefore, the existing digital exposure apparatuses have used a method in which individual controls are impossible.
According to the related art maskless exposure apparatus, when a light condensing lens unit is used, there is a limitation in obtaining high resolution due to the non-uniformity of focus and light amount of each lens included in the light condensing lens unit.
In case of a digital exposure apparatus using a spatial light modulator, the alignment between the spatial light modulator and a light condensing lens unit requires a considerably fine level in order to implement high resolution. However, it is very difficult to implement a very precise alignment between units produced through physically different processes. Since a focus is formed on a final photoresist (PR) surface due to light interference caused by a substantial cross-talk, intensity of illumination is not uniform, and resolution is degraded.
Therefore, it is required to develop a method for ensure high resolution of an exposure pattern by easily correcting the alignment between a plurality of optical equipments included in a maskless exposure apparatus.